The automobile blade-type plug-in fuse disclosed in U.S. Pat. No. 4,635,023 is a two-piece assembly having a thin, box-like housing and a plate-like, all metal plug-in fuse element secured therein. The metal plug-in fuse element has a pair of spaced, confronting, exposed terminal blades extending from one side of the housing. These terminal blades plug into pressure clip socket terminals. Current-carrying extensions of the terminal blades extend into the housing where they are closely encompassed by the housing walls. A fuse link unsupported between the ends thereof extends suspended between the current-carrying extensions and is spaced from the housing side walls.
The fuse link of this and other types of fuses including the fuses of the present invention melts and sometimes vaporizes under fuse blowing conditions. These fuses generally are designed to blow under both prolonged modest overload current like 135% of rated current within 1/2 hour or instantly under short circuit current. Under such a prolonged modest overload current the temperature of the fuse link progressively rises until the fuse opens the circuit involved. The temperature rise in the fuse link results from electrical power dissipation in the electrical resistance R of the fuse link material due to electrical current I flow therethrough. The formula describing this power dissipation P is P=I.sup.2 R.
Under normal operation (normal current is usually about 70% of rated current), the heat dissipated in the fuse link is sufficiently small that a large section of the fuse link does not melt or even soften. Heat generated in the fuse link is conducted into the terminal blade portions, housing and panel socket clips. When a current substantially above rated current (like 135% thereof) flows in the link, the heat dissipation is such that there is an insufficient rate of conduction of heat therefrom so that the temperature rises to the temperature which melts the fuse link. The fuse link will soften before it melts, and it is important to the reliability of the fuse that before melting the fuse link does not soften to a degree that the outer portions of the link become so weakened that the center portion sags against a side wall of the housing before the desired fuse blowing conditions occur. If this occurs, the contact made between a sagging fuse link and the housing can melt the fuse housing and cool the fuse link and prevent it from blowing in the desired time period or from blowing at all.
The fuse disclosed in U.S. Pat. No. 4,635,023 was designed to overcome this sagging problem which is not expected to be a problem with fuses carrying 100 amps and above where the material of the all metal portion of the fuse involved is made of copper instead of a soft metal like zinc. The teachings of this patent would not, therefore, be expected to be applicable to fuses carrying rated current of 100 amps and above. If one chose to use the fuse design disclosed in this patent to carry such rated currents by increasing the size, thickness and mass of the various portions of the fuse thereshown, the resulting size of the fuse and plug-in socket terminals would be undesirably large.
One of the objects of the present invention is to provide an automotive fuse which can be inexpensively manufactured, and will be of a smaller size than the modified fuse just described.